A conventional display consists of a projector and a screen. The problem with conventional projectors is that they are not bright enough. Typically, only about 5% of the light from the projector lamp reaches the screen. The other 95% of the light is lost inside the projector.
One exemplary type of conventional projector used for high ambient light environments is the liquid crystal light valve projector. Light from the projector lamp is collimated and linearly polarized prior to illuminating the liquid crystal video display. Next, the light passes through a second polarizer (called an analyzer). The analyzer polarization axis is rotated 90 degrees with respect to the light polarization axis. Thus, the light is blocked. However, activating the liquid crystal causes the light polarization axis to rotate which allows some of the light to pass through the analyzer. The greater the activation of the liquid crystal, the greater the rotation of the polarization axis of the light and the greater the percentage of light that passes through the analyzer. In other words, the liquid crystal is not activated in the regions of the video display that are black. The liquid crystal is activated to its maximum in the regions of the video display that are white. Most of the 95% light loss occurs in the collimation optics and two polarizers. A high degree of collimation is required; otherwise the liquid crystal does not function properly. The brightest liquid crystal light valve projectors output approximately 3,500 lumens. For a 9.times.12 foot display with a screen gain of five, the display brightness is only 160 foot Lamberts. This is too low for high ambient light environments (10,000 foot Lamberts).
Another type of projection apparatus designed for outdoor electronic signs uses a matrix of miniature projection-type cathode ray tubes (CRTs). While this type of projector produces a bright display, there are high cost and maintenance problems associated with miniature CRTs.